A toothed belt is widely used in an internal combustion engine to transmit the motive power from a crankshaft to a camshaft. Generally, a heavy load acts upon the toothed belt used in the internal combustion engine so that the life of the toothed belt tends to be relatively short. Recently, internal combustion engines are being downsized, and as a result, the width of toothed belts is also being reduced, so that heavier load acts on the toothed belt. Accordingly, the operating life of the toothed belt tends to be reduced, and moreover, noise is also more likely to be generated when the belt is engaged with a pulley and the like.
As a method for extending the belt life, emphasis may be placed on the rigidity of the belt teeth by improving the modulus of the tooth rubber. However, noise generated by the belt under operating conditions becomes more likely when the rigidity of the belt teeth is increased. In particular, internal combustion engines are often operated in a high-temperature environment (e.g., about 100-120° C.), and in such an environment noise performance and durability performance are likely to decrease.
In Patent Document 1, there is disclosed a high-density polyethylene that contains 20 percent by weight of high-density polyethylene having a cross-linkable part is compounded with a rubber composition to improve the properties for low heat build-up, heat resistance, high hardness and permanent set-in fatigue without compromising the fracture characteristics. However, in Patent Document 1, application of the high-density polyethylene to a belt is not suggested. Further, it is conceivable that improvement of noise performance during belt operation would be difficult by simply applying the rubber composition of Patent Document 1 to a belt, because hysteresis loss (tan δ) is mitigated by cross-linking the high-density polyethylene to acquire the low heat build-up property.